This invention relates to a tracking error signal producing arrangement for use in a tracking control device for controlling an optical disk device. This invention relates also to the tracking control device.
The optical disk device comprises an optical information recording disk having a principal surface and grooves formed on the principal surface for defining information recording tracks extended across a radius of the optical information recording disk. The information recording tracks are arranged on the principal surface with a predetermined track pitch. An irradiating unit irradiates a part of the principal surface by an optical beam to make the part reflect the optical beam as a reflected light beam having first and second partial light beams. The first and the second partial light beams result from first and second fractions of the part. The first and the second fractions appear by dividing the part radially of the optical information recording disk. First and second photoelectric sensors receive the first and the second partial light beams to produce first and second electric output signals, respectively. An actuating arrangement actuates the irradiating unit in compliance with a control signal to move the irradiating unit radially of the optical information recording disk.
The tracking error signal producing arrangement is connected to the first and the second photoelectric sensors. The tracking error signal producing arrangement is for producing a tracking error signal in response to the first and the second electric output signals. The tracking error signal indicates a positioning error of the optical beam with respect to a particular one of the information recording tracks in a radial direction of the optical information recording disk.
The tracking control device comprises a control signal producing arrangement connected to the tracking error signal producing arrangement. The control signal producing arrangement produces the control signal in compliance with the tracking error signal to make the actuating arrangement actuate the irradiating unit so that the tracking error signal becomes to indicate the positioning error equal to zero. As a result, the irradiating unit irradiates the particular one of the information recording tracks by the optical beam.
The tracking error signal producing arrangement is disclosed in U.S. Pat. No. 4,914,725 issued to Karl A. Belser et al. The Belser et al tracking error signal producing arrangement comprises a subtracter connected to the first and the second photoelectric sensors for subtracting the second electric output signal from the first electric output signal to produce a subtracted signal which is for use as the tracking error signal.
As will later be described, the subtracted signal has an amplitude which varies in compliance with a sinusoidal curve to indicate the positioning error while the irradiating unit is moved radially of the optical information recording disk from a periphery of the optical information recording disk towards a center axis of the optical information recording disk. More specifically, the subtracted signal has an amplitude equal to zero to indicate the positioning error when the irradiating unit irradiates a center line of the particular one of the information recording tracks. When the irradiating unit irradiates an inside one-quarter track position which is apart from the center line of the particular one of the information recording tracks towards the center axis of the optical information recording disk by a quarter of the predetermined track pitch, the subtracted signal has a maximum amplitude greater than zero to indicate the positioning error. When the irradiating unit irradiates an outside one-quarter track position which is apart from the center line of the particular one of the information recording tracks towards the periphery of the optical information recording disk by a quarter of the predetermined track pitch, the subtracted signal has a minimum amplitude less than zero to indicate the positioning error.
Thus, the subtracted signal used as the tracking error signal approximately and linearly increases to precisely indicate the positioning error of the optical beam with respect to the particular one of the information recording tracks while the irradiating unit is moved radially of the optical information recording disk from the outside one-quarter track position to the inside one-quarter track position. However, in a case where the irradiating unit irradiates a part of the principal surface except an extent between the outside and the inside one-quarter track positions, the subtracted signal does not precisely indicate the positioning error with respect to the particular one of the information recording tracks in the manner which will become clear as the description proceeds. When the subtracted signal is used as the tracking error signal in the above-mentioned case, the tracking control device inevitably makes the actuating arrangement actuate the irradiating unit so that the irradiating unit irradiates by the optical beam a different track adjacent to the particular one of the information recording tracks rather than the particular one of the information recording tracks.
It is required to obtain a precise tracking error signal precisely indicating the positioning error of the optical beam with respect to the particular one of the information recording tracks even when the irradiating unit irradiates a part of the principal surface except the extent between the outside and the inside one-quarter track positions. Although the Belser et al disclose an adder connected to the first and the second photoelectric sensors for adding the second electric output signal to the first electric output signal to produce an added signal, the added signal is not used in compensating for the subtracted signal to obtain the precise tracking error signal.